If your treeview has to display a lot of nodes, populating the treeview with all of them is not a good idea in a web-context since this may produce a lot of HTML and ViewState, effectively rendering the treeview useless. That's why, RadTreeView now supports the NodeExpand server event that fires a server-event for a node, so that developers may add nodes on the fly per their own requirements.

This example demonstrates this for Sql DataSource - a single self-referencing table (Id -> ParentId).